Internal combustion engines create drive torque that is transferred to a drivetrain via a crankshaft. Some internal combustion engines include engine control systems that deactivate cylinders under low load situations. For example, an eight cylinder engine can be operated using four cylinders to improve fuel economy by reducing pumping losses. This process is generally referred to as displacement on demand or DOD. Operation using all of the engine cylinders is referred to as an activated mode. A deactivated mode refers to operation using less than all of the cylinders of the engine (one or more cylinders not active).
During engine operation a cylinder or cylinders may misfire. After a misfire occurs, the engine RPM decelerates until other firing cylinders produce enough power to stabilize the engine. During the activated mode, the engine behaves in this manner, but only to a limited extent since the cylinder after a misfiring cylinder is also active and is doing work. During the deactivated mode, the cylinder that is after a misfiring cylinder also does not fire because it is deactivated.
Traditional misfire detection systems do not account for the deactivated cylinders. As a result, false misfires can be detected, which result in increased warranty costs, increase the complexity in analyzing an actual cylinder misfire and detracts from overall vehicle performance and customer satisfaction.